Total hip replacement (THR) surgery is the standard of care for advanced degenerative joint disease in the US. In 2002, an estimated 243,000 Americans benefited from this procedure. However, 18% of all THR surgeries are revisions, which have poorer outcomes and greater economic burden than primary THRs. Loosening of hip implants, due to osteolysis and tissue reactions to polyethylene wear debris, is considered to be the main problem limiting implant longevity in the US. Within the past decade, polyethylene materials used for THR have undergone major changes in sterilization and formulation, so that a range of sterilization and radiation crosslinking processes are now applied to polyethylene used in clinical practice. However, it remains unclear to what extent these processes affect the tendency of polyethylene bearing components to oxidatively degrade during long-term implantation in the body. It is further unknown to what extent oxidation of polyethylene in the body impacts the clinical performance of contemporary hip replacements. In this five-year competing continuation, we propose to extend our study of traceable gamma-air sterilized polyethylene hip bearing components to encompass retrieved gamma-inert sterilized and highly crosslinked polyethylene bearings for hip arthroplasty. Knowing that gamma air-sterilized polyethylene hip bearing components undergo in vivo oxidative degradation with significant reduction of ultimate strength, the following three new hypotheses are proposed: (1) contemporary gamma inert sterilized polyethylene hip bearings will undergo {region-specific} degradation of mechanical properties during in vivo use; (2) annealed highly crosslinked, polyethylene hip bearings that contain residual free radicals will undergo {region-specific} degradation of mechanical properties in vivo and remelted highly crosslinked polyethylene hip bearings, that are processed to quench free radicals, will not degrade significantly in vivo; and (3) wear and loosening as reasons for revision of highly crosslinked liners will be lower in prevalence than in gamma inert sterilized liners. [unreadable] [unreadable]